CURRENT ELECTRICITY Flashcards
Define current.
Current is a measurement of the charge flowing past a point each second.
I = ^Q/^t
Define Potential Difference.
Is a measurement of the energy transferred between two points per unit.
V = W/Q
Give the equation of power.
Power = ^W/^t
P = IV
Give the rules of a series circuit.
Current = same everywhere.
Potential difference = across the individual components adds up to the total p.d. of the supply.
Give the rules of a parallel circuit.
Current = current into the junction equals current out of a junction.
Potential difference = same across all components.
State Ohm’s Law.
Current through a conductor is directly proportional to the potential difference across it, provided temperature and other physical conditions stay constant.
What is a ohmic conductor?
One where I is proportional to V.
What is a non-ohmic conductor?
One where I isn’t proportional to V.
What is Kirchhoff’s 1st Law.
Sum of all the currents at a junction is zero.
What is Kirchhoff’s 2nd Law?
Sum if the emf’s is equal to the sum of the potential difference around a closed circuit loop.
Describe resistors.
On a I against V graph it is a straight line. If the resistance larger then less current would flow out with the same p.d as another resistor so the line would be less tall.
Are ohmic conductors as I proportional to V
Describe Filament Bulbs and explain their shape.
Is a straight line until 0.4 V and then curves towards the V axis until 8.0 V. Then is curves slightly up.
Shape of the curve the same in positive and negative quadrant because doesn’t matter which direction current flows.
Graph is a curve as with increasing current filament gets hotter which increases resistance so for equal increase of p.d. there is a smaller increase in current.
Explain how resistance of a filament bulb increases with temperature.
Because there are more collisions between electrons and atoms (in filament)
Describe Thermistors.
Thermistors are “semi-conductor” materials which have a few charge carries ie electrons.
As heated up, more electrons are released making it easier for current to flow hence resistance decreases.
Describe shape of thermistors held at constant temperature.
On a I against V graph it is a straight line. Thermistors at higher temperatures have a lower resistance therefore a higher current at the same p.d.
